As an elastic hollow organ, the primary function of the urinary bladder is to store urine until it is emptied through the urethra. The urinary bladder can be affected by many different disorders of psychological and/or somatic origin.
What is the urinary bladder?
Schematic diagram showing the anatomy and structure of the urinary bladder. Click to enlarge. The urinary bladder (vesica urinaria) is the name given to an expandable muscular hollow organ that rests on the pelvic floor in the lesser pelvis immediately behind the pubic bone (OS pubis) and serves to receive and temporarily store urine. When empty, the urinary bladder is compressed like a limp sac by the viscera in the abdomen. If the vesica urinaria slowly fills with urine, which passes from the renal pelvis into the bladder body of the hollow organ via the two ureters, it expands in a spherical shape as the volume fills. In women, the urinary bladder borders the uterus (womb) at the back of the pelvis, while in men it closes off to the rectum (rectum).
Anatomy and structure
The urinary bladder is located in the lesser pelvis, where it attaches to the pubic symphysis and extends upward to the upper edge of the pelvis. It can be divided into distinct areas. The cranial (upward) area has a peritoneal covering (serosa or peritoneum) and is also called the apex vesicae. The actual bladder body (corpus vesicae), in which the urine arriving from the kidneys is temporarily stored, lies directly below and is bounded downward by the base of the bladder (fundus vesicae). On the lower side there is also the cervix vesicae (bladder neck), which tapers funnel-shaped towards the urethra. The orifices of the paired ureters and the exit of the urethra form the so-called trigonum vesicae (bladder triangle). In the area of the urethral orifice, the urinary bladder has an internal and external sphincter (sphincter muscles), whereby only the external striated urethralis muscle is subject to conscious control by humans. The urinary bladder is further anchored to the pelvic floor by various ligamentous serosa duplications (peritoneal folds). From the inside, the urinary bladder is lined by a layer of mucus as protection against urine. In contrast, the outer layer of the urinary bladder is composed of smooth muscle (detrusor).
Functions and tasks
As a hollow organ, the primary function of the urinary bladder is to provide intermediate storage for secondary urine from the kidney until it is emptied through the urethra. The distensibility of the urinary bladder ensures that it can hold between 900 to 1500 ml of urine, with the urge to urinate occurring in an adult from about 300 to 500 ml. During emptying (micturition), smooth muscles (detrusor) of the urinary bladder contract while sphincters at the base of the bladder relax, forcing urine out of the lumen via the urethra. Although the kidneys continuously drain urine into the bladder via the ureters, voluntary emptying is ensured from time to time by the external sphincter, which is subject to conscious control by the individual, although the accompanying processes are reflexive. With increasing filling volume, the bladder wall stretches and tenses, which is perceived by the stretch sensors located in the wall, which trigger the so-called micturition reflex in the parasympathetic centers of the spinal cord. These in turn cause contraction of the smooth muscles of the bladder wall (Musculus detrusor), which, with simultaneous relaxation of the external striated sphincter, leads to outflow of urine through the urethra. This process is further assisted by contraction of the abdominal and pelvic muscles.
Diseases
The urinary bladder can be affected by a variety of acquired or genetic impairments. One of the most common bladder diseases is cystitis or cystitis, which is generally due to an infection that ascends through the urethra. Women are particularly affected by cystitis due to their shorter urethra. A dysfunction of the closing mechanism can cause urinary incontinence (involuntary leakage of urine), which can be triggered by psychological (stress) or physiological factors such as paraplegia, detrusor-sphincter dyssynergia or Parkinson’s disease. A cystocele is a protrusion of the urinary bladder into the anterior vaginal wall in women.It occurs in connection with pelvic floor weakness, usually combined with a lowering of the vagina. Urinary retention due to prostatic hyperplasia can lead to overdistension of the bladder (vesica gigantea) as well as incomplete bladder emptying (residual urine). Clinically relevant residual urine is also a symptom of strictures, stenoses or benign hyperplasia or malignant prostate carcinoma. Tumor diseases of the bladder are very common in Germany and are among the most widespread types of tumor, with urothelial carcinomas (malignant tumors of the mucous membrane of the bladder) accounting for 95 percent of all cases. If there is a permanent state of irritation, for example as a result of hypothermia, we speak of an irritable bladder, in which even small amounts of filling trigger the micturition reflex. In addition, a bar-like hypertrophy (thickening) of the bladder muscles (so-called bar bladder) leads to reduced contractility, which can cause residual urine formation and urinary tract infections. External trauma (force), in addition to pelvic fracture, can lead to rupture of the urinary bladder (urinary bladder rupture) with symptoms such as lower abdominal pain and urge to micturate with concomitant urinary retention.
Typical and common bladder disorders
- Bladder infection
- Incontinence (urinary incontinence)
- Nocturnal urination (nocturia)
- Bladder weakness
